The usefulness of the phenomenon of magnetostrictivity in linear distance or position measuring devices is recognized by the prior art; for example, see Redding, U.S. Pat. No. 4,305,283; McCrea et al, U.S. Pat. No. 4,158,964; Krisst, U.S. Pat. No. 4,071,818; Edwards, U.S. Pat. No. 4,028,619; and Tellerman, U.S. Pat. No. 3,898.555. Common to several of these devices are a magnetostrictive wire that runs in a straight line path through the measurement field, means for inducing a torsional strain at a given position along the wire, and a magnet that is displaceable along the wire, either by connection to a movable body such as a machine tool or by reason of association with a float device. Generally speaking, the position of the magnet represents the position of the monitored quantity and is determined as a function of the time required for a torsional strain to propagate from one end of the wire through the area of influence of the magnet or from the position of the magnet to a sensing apparatus located at one end of the wire.
Prior art magnetostrictive position detectors employing magnetic transducers typically use side mounted coils. Such sensing coils must be carefully located to be near a null in the magnetic field induced by the electrical transmission pulse. Otherwise the relatively large magnetic field induced by the electrical transmit pulse would overload the high gain amplifier connected to the sensing coil. This prior system results in a long settling time error at the amplifier creating a long dead band following initial transmission. Location at a magnetic null reduces this settling time. However, determination of the location of such a magnetic null is a difficult process that must be repeated for each design. In addition, the prior system can be adversely affected by small position changes of the sensing coil. Therefore there is a need in the art for transducers used with magnetostrictive position detectors that provide immunity to overloading during electrical excitation of the magnetostrictive wire.